Of surface level control valves in fuel tanks, there is one, as shown in FIG. 16, in which a valve member 101 is coupled to the upper part of a float 100 to be capable of relative movement, and it is made such that this valve member 101 is pushed upward by a protruding part 100a formed in the center of the upper part of this float 100, and this valve member 101 is made to contact with a seat part 103 provided inside an air exchange passage connecting to a canister, and it closes this air exchange passage in this state of contact (see Patent Document 1).
However, in such control valve, first, it functions such that the float 100 descends when the surface level drops from the closed state of the air exchange passage, and at this time, the edge part of the head part on the upper part of the float 100 catches on a protrusion 101a of the valve member 101 and moves the valve member 101 away from the seat part, but when a force is applied to the valve member 101 so as to stick to the seat part 103, such as when the inside of the fuel tank is under high pressure, it is difficult to pull the valve member 101 immediately from the seat part 103 by the descent of the float 100, and it is difficult to release the closure of the air exchange valve with good response when the surface level goes down.
Also, second, the valve member 101 is supported by said protruding part 00a, but when the valve member 101 is tilting during ascent of the float 100, it comes to contact first with the seat part 103 on the upward side of the tilt of the valve member 101. Also, in this case, the downward side of the tilt of this valve member 101 is finally lifted up and the posture of the valve member 101 is corrected, but because this correction is accomplished by making the edge part 100b of the head part on the upper part of the float 100 and the inner surface of said protrusion 101a contact on the downward side of the tilt of the valve member 101 away from the center of the float 100 (FIG. 16), when done thus, the force necessary to make the valve member 101 contact completely with the seat part 103 is made excessively great.    Patent Document 1: Publication of Japanese Unexamined Patent H7-279789